\begin{table}[htbp]\centering
\def\sym#1{\ifmmode^{#1}\else\(^{#1}\)\fi}
\caption{Estimated  Effect of Quarter Until Election on Event-Fundraising Proportions}
\begin{tabular}{l*{3}{c}}
\hline\hline
                &\multicolumn{1}{c}{(1)}&\multicolumn{1}{c}{(2)}&\multicolumn{1}{c}{(3)}\\
                &\multicolumn{1}{c}{All Candidates}&\multicolumn{1}{c}{Incumbent Candidates}&\multicolumn{1}{c}{Non-Incumbent Candidates}\\
\hline
Quarters Until General Election&     1.79\sym{***}&     2.52\sym{***}&     0.70\sym{***}\\
                &   (0.10)         &   (0.14)         &   (0.14)         \\
Constant        &    23.14\sym{***}&    27.64\sym{***}&    20.47\sym{***}\\
                &   (0.24)         &   (0.39)         &   (0.30)         \\
\hline
Observations    &    41965         &    18102         &    23831         \\
\hline\hline
\multicolumn{4}{l}{\footnotesize Standard errors in parentheses}\\
\multicolumn{4}{l}{\footnotesize \sym{*} \(p<0.10\), \sym{**} \(p<0.05\), \sym{***} \(p<0.01\)}\\
\end{tabular}
\end{table}
